Damsels and Dragons - the
Insect Order Odonata
The Odonata (from the Greek odon-o meaning
tooth), commonly known as dragonflies and damselflies, is a
fascinating insect order. (In some areas, the term dragonfly is used
for both groups.) Since this article is for the Internet Pond
Society, I have emphasized pond species and activities that the
reader, as a pond owner, might observe or perform.
Some of the images used here are linked from other web
pages where the reader will find additional information, pictures or
links. All sites were active when the article was submitted (Jan 31,
1997). Unless otherwise indicated all photographs are by the author
( details on the reproduction techniques and use
restrictions)
Introduction
Dragonflies and damselflies are insects. As such,
they have 3 prominent body parts - a head, a thorax to which the
wings, in this case 4, and 6 legs are attached, and an abdomen.
Their front and rear wings are not linked together, but can be
operated independently. The dragonfly is an impressive insect, a
master of the air, daring enough, in some cases, to hover almost
within arm's reach in front of human invaders in its territory. At
rest, its wings lie flat, at right angles to the body. The damselfly
is generally much less impressive or conspicuous. It tends to be
smaller and less robust, a much weaker flyer still capable of aerial
acrobatics, but less active. At rest, damselflies hold their wings
over their backs, either together or spread out in a v-shape.
Damselflies usually stay close to a surface, while dragonflies can
zoom up into the air and out of sight. Dragonflies and damselflies
are predators throughout their lives.
Dragonflies and damselflies have been around for a
long time. Impressive fossils of dragonflies with 27" wingspans have
been found dating back over 200 million years. Today, the largest
ones have wingspans about 5 to 6 inches.
As with many insects, dragonflies have played a
significant role in some cultures. An article by Montgomery
in 1972 lists 95 English terms used for dragonflies. With the
current interest in topical postage stamps, there are now over 100 stamps from around the world that
feature dragonflies either as the main design or a decorative
addition.
Among the Odonata there is an amazing amount of
variation, both in their life histories and their activities. These
fascinating insects which fly around your pond for a short period
are much older than you might think. Most of them have spent a much
longer period of time as important aquatic predators.
Mating
Appendages that can be seen at the end of abdomen of
the male are designed to lock into species-specific grooves and
notches on the female in order to secure the two together for
mating. The features on female dragonflies may be on the head alone
or on the head and the front segment of the thorax. Female
damselflies have features on the front segment of the thorax. Male
and female dragonflies tend to wed in the air, sometimes with an
audible impact. Damselflies become hitched together more quietly,
often coming together on vegetation. Hitched pairs, particularly
damselflies (just because they are generally more numerous), can
often be seen flying about "in tandem" looking for mating sites.
tandem pair flying over open water (you can see the
reflection)
The mating formation is called a wheel.
Attached to the male by her head and/or the front segment of her
thorax, the female curls her abdomen under her, reaching forward
with the tip of her abdomen in order to pick up the sperm from the
male's second abdominal segment. From the side, damselfly pairs
appear sort of heart-shaped. Some dragonflies mate in the air, while
others alight to mate (this may be the only time you get a good view
of some species). Damselflies usually land to mate. In species that
land, you can often see the legs of the female wrapped around the
abdomen of the male for strain relief and support during mating. The
male may assist the female by moving or curling his abdomen.
Previously mated males can be distinguished if their abdomens have
become damaged (dented) from the downward pressure of the females'
legs. For some species, the mating time is very short, only a few
seconds. For others, especially some of the damselflies, it can be
up to several hours. (Perhaps this is why,
Martin Peterson found that they were
once regarded as a symbol of the love goddess, Freya.) Males and
females of some dragonflies can be seen flying "in tandem" after
mating, but this activity is more common among the damselflies.
Inter-specific sexual activity is normally discouraged
by the lock-and-key aspect of the attachment process (it has been
reported). Damage incurred from prior mating activity can allow some
inter-specific activity.
Egg Laying
Depending on the species and/or the circumstances,
the male may or may not be around while the female lays her eggs.
Males can often be found guarding the female, chasing off other
potential mates so that she can finish laying the eggs fertilized
with his sperm. Some species go to extremes in mate guarding - the
male doesn't release the female, but remains attached until she has
laid at least some eggs. Tandem pairs can often be seen flying
slowly among the vegetation, looking for oviposition sites.
For many species often seen in tandem, the female
inserts each egg individually into some suitable vegetation, from
dead wood to reeds, sometimes above the waterline, sometimes below,
sometimes so far below that the males and females descend into the
water breathing via a protective coating of air that gets trapped in
the many fine hairs on their bodies. In cases where the eggs are
laid above the waterline, several situations may occur. Sometimes
the eggs are laid over water, and the newly emerged larva drops in.
Sometimes, the vegetation dies and falls into the water, or becomes
submerged after the rains.
Archilestes californica (damselfly) tandem pair
laying eggs
In
D. Paulson's copyrighted image
available through the University of Michigan, 6 pairs
of the damselfly,
Argia moesta, are ovipositing. In this
case, the females generally have their abdomens seeking sites in or
near the water while the males are approximately vertical.
In many cases where the female lays her eggs with
the male nearby or absent, the female hovers over a suitable
location, descending periodically to dip the tip of her abdomen into
the water and wash the eggs off. The females of some species scatter
their eggs from the air. Females have been known to become confused
and attempt to lay eggs on unsuitable substrates such as oil and
windshields.
If you are interested in allowing these creatures some
space in your pond, observe where egg laying is occuring and make
some allowance for this when you perform any maintenance. There may
be preferred sites, some of which might include the more tropical
plants in your pond (i.e. the ones you might take inside to
overwinter).
Larvae
After the egg has hatched, the larva (also called a
nymph or naiad) is a crytically colored, free living, aquatic
predator. Larvae prey mainly on other aquatic insects, such as
mosquito larvae or even other odonate larvae. Larger larvae may prey
on fish fry. In turn, dragonflies are preyed on by a number of
species, including fish and frogs. They may serve as hosts for
certain aquatic mites and avian parasites. Many species live among
the aquatic vegetation.
A damselfly larva is characterized by 3 fin-like
appendages, called lamellae, at the end of its abdomen, The lamellae
are important for respiration.
damselfly larvae in water (Ohio Dept. of Natural Resources
photo.)
(from the Rivers Online - Darby Creek
Site)
Compared to damselfly larvae, dragonfly
larvae are broader and less delicate looking. Dragonfly larvae lack
the lamellae of the damselflies, relying on foliations in the rectal
area for respiration.
larva for a dragonfly known as the Green Darner
(from
a Texas A & M study by Dr. Ann
Kenimer on the Texas Water Resources Institute web
site)
dragonfly larvae similar in appearance to those of many pond
species
(from Texas A & M study by Dr. Ann Kenimer indicated
above)
As with all insects, the larvae undergo a
series of molts as they grow and develop. While some species have
relatively short larval development times (1-2 months from the egg
hatching to emergence), most spend at least a year and some much
longer (5 years or more in places where the climate is arduous) as
aquatic larvae. Most will spend at least one winter in your pond and
have to suffer through any maintenance activities you perform. Some
may not survive activities such as cleaning the "mulm" from your
pond.
Emergence
Dragonfly and damselfly larvae are aquatic
creatures. At the end of the final larval stage, the nymph climbs
out into the air, perhaps onto a stone, or a plant stalk, or even
some algae floating at the surface. Its position stabilized, the
insect splits this last larval skin open along a suture on the back
of the thorax and pulls itself out through this hole. The exact
details of extraction vary with the orientation of the larval skin.
Odonate development lacks the familiar pupal stage (e.g. chrysalis
of a butterfly). By the time the larva leaves the water, an adult,
albeit a rather uninflated one, exists inside the skin which is
about to be shed.
a stream species tranforms on a vertical rock
face
The empty larval case, called the exuvia, is hidden mainly
in the shadow.
The crumpled features on the back of the thorax
are the unexpanded wings.
After the insect has extracted itself, a
period of time, usually a couple of hours or so, elapses during
which the body and wings expand and cure sufficiently to withstand
flight. Emergence is not an easy process, and the insect is
incredibly vulnerable as it prepares for life in an entirely new
medium. Many things can go wrong, and sometimes do. Weather changes
can have disastrous results. Winds and rain can cause irreparable
damage by bringing things into contact with the developing body or
wings. The insects can become dislodged, falling into the water
where they can drown or be eaten. Where suitable emergence sites are
limited, larvae can walk over one another disrupting development.
During emergence, the insect can't fly away, and hence is vulnerable
to numerous predators. Emergence requires a lot of energy and some
insects die trying.
this dragonfly (Libellula quadrimaculata) had
a very hard emergence
The front wings appear to be undamaged, but
the back wing
on the left appears to have gotten folded over and
the one
on the right appears to have been broken. The abdomen is
also malformed, having a segment which twists to the
left.
(You probably won't see a picture like this in any books.)
The date and time that emergence takes place
tends to be species related but can be affected by recent weather
conditions (especially the temperature). The damselflies I am
familiar with tend to emerge in the morning and fly in the early
afternoon.
After curing sufficiently (perhaps a bit earlier if it
is disturbed), the insect, now in its more familiar dragonfly or
damselfly form, makes its maiden flight, away from the water.
Compared to the mature adults you might be familiar with, insects
which have just completed their emergence lack the vibrant colors
(especially noticeable in the eyes). Their wings have a higher
gloss, as though covered with cellophane/saran wrap and look more
fragile. The maiden flight is generally short (more like a hop) and
does not appear strong or well coordinated - the flight muscles are
weak and the thoracic skeleton has not fully hardened. Recently
emerged insects are often snapped up by hungry or nesting birds.
Most of the pond or quiet water species I am familiar
with usually emerge on vegetation in or near the water. If you are
lucky, you might see a nymph climbing out of the water. I usually
find them after their transformation has started, usually long
after. Emergence is a treat to watch, but make yourself comfortable,
most things don't happen very quickly. Take pictures if you want,
but try not to disturb the insect for it is tired and vulnerable.
Also, take care of yourself, emergence seldom takes occurs in a
convenient place.
You can monitor the production of your pond by
collecting the empty larval skins, or exuviae, on a regular basis.
Examine the emergent vegetation and other suitable substates like
sticks and rocks. If you find an exuvia, check that it is empty.
Whitish strands can usually be seen sticking out of the hole through
which the insect got out. These strands are the remains of the old
tracheal linings. Check that the insect has actually left the
vegetation - it may just have moved up to catch more sunlight.
Collect these empty skins by gently sliding them up the vegetation,
or prying them off the substrate. Be careful, they are very light
and easily carried away by any breeze. If the wind has been blowing
you may find some of the empty skins in the water, but they can
remain attached to the substrate for some time. Sorting these by
appearance will give you an idea how many species are using your
pond. (Remember that there are other kinds of insects that have an
aquatic larval stage.) Record the numbers by date to give yourself
an idea of the cycle of emergence. Probably you will not see some
exuviae that are hidden or inaccessible, but this will give you some
indication about what is there.
Maturation
Having emerged from the water and attained its
aereal form, the resulting dragonfly or damselfly spends some time
away from the water while it matures sexually. This period generally
ranges from a few days to a couple of weeks, but can be longer in
species that migrate. During this time, the body and wings harden,
and the color becomes more vibrant. The males of some species
undergo dramatic color changes during this period. This is also a
period of high mortality. In cooler areas, individuals may be
attracted to the warm surface of asphalt roads and killed or stunned
by passing cars and trucks.
When they return to the water they are ready to mate.
Adult Behaviour
Adult odonata feed mainly on other insects such as
small gnats, mosquitoes, black flies, horse flies, and deer flies.
(Many a beleagured north woods hiker has expressed gratitude and
encouragement to feeding dragonflies.) Some even feed on other
dragonflies or damselflies. Most species hunt mainly during the day,
but a few species are crepuscular (evening) hunters. I would not be
surprised to find some daytime hunters regularly around bright
lights in the evenings, but I personally don't know of this
happening.
One interesting behavioral aspect that you can observe
for dragonflies which perch regularly is their postures. Dragonflies
can adjust their orientation, body position and wing positions to
regulate their body temperature. Sometimes a dragonfly will position
itself so that the tip of the abdomen is pointed at the sun and the
wings are rotated down and tipped forward to shade the thorax. The
surface of the body exposed directly to the sun is thus minimized.
When the sun is high in sky, the dragonfly is almost standing on its
head and this extreme position is called the "obelisk" posture. Why
doesn't the dragonfly just move to a shady spot? If the insect cools
too much, it only needs to adjust its wings or body. If it has moved
it will need to move back, and this uses up energy.
Identification
Dragonflies and damselflies have numerous species
specific requirements. The ones around your pond will usually have
an aquatic stage that can tolerate the climatic conditions in your
area and pond. There are a number of species that seem to prefer the
acidic water conditions of bogs and fens. A number of species prefer
the running water of streams, or rivers. A number of other species
prefer ponds or slowly moving water. Many of these pond species can
be identified from a distance, but it does take lots of practice.
Field guides are available for some areas.
a common pond dragonfly in the southwest U.S., Libellula
saturata, basking in the sun
The species of dragonflies that prefer ponds
belong mainly to the family Libellulidae, often called skimmers in
field guides. Many of these are territorial, hunting from favorite
perches along the water. They can be quite active in the warmer
weather. A number of these are brightly colored, the males and
females sometimes looking considerably different. Many have
conspicuous color markings on their wings. The libellulids are among
the easiest dragonflies for the beginner to identify because of
their coloration, and their perching habits, often right out in the
open. The males tend to be more noticeable. (General insect guide
books don't always distinguish between males and females in their
pictures.)
Dragonflies can be quite tolerant of photographers,
but it is generally a waste of time and energy to attempt to
photograph a reluctant individual. One key area used in
identification in the texts is the venation pattern of the wings.
For libellulids, some veins in the rear wing form a characteristic
boot-shaped pattern - toe down. For many non-libellulids, a picture
or some idea of the species dependent appendages on the male may be
necessary for a positive identification.
Unarguably the best dragonfly pictures currently on the
web, these scanned dragonflies, while limited in
number, can be used to examine wing venation and color patterns.
Look these pictures up. There are a number of damselfly species that
occur around ponds. Being smaller, these are harder to photograph
reliably. The appendages on the male are the best characterisitics
for identification, but the worst to try and photograph. Many of the
species look similar, and may not be separable photographically
without experience or a photographic reference collection. The
patterns on the males and females often differ, so it helps if you
can photograph the two together.
Unlike butterflies, there is little color or pattern
variation between members of one species. The bright colors of dead
specimens fade quickly unless they are properly preserved - even
then they are not as brilliant as in life.
Conclusions
Dragonflies and damselflies are exciting creatures
to study. Use your web pages to document the activity you observe.
Anecdotal information seldom makes it into the literature, or is
difficult to find. Wetlands, even small ones, are an important
component of world around us.
further information and links
Disclaimer
This article is based on published material and
personal experience. While I study dragonflies and damselflies
whenever I can, I am an amateur entomologist (i.e. a person who
studies insects) and a photographer, rather than an insect
collector. Errors in presentation or interpretation are mine alone.
Ron Lyons (volunteer
1990-1999)
Chula Vista Nature Center, 1000 Gunpowder Point Drive,
Chula Vista, CA 91910-1201
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